Generally, in a vehicle equipped with an internal combustion engine, heat generated in the engine is transferred to a cylinder head, a piston, a valve, and so on. If the temperature of the above components excessively increases, the material strength thereof will be lowered to cause failure or shorten the life span. Therefore, a cooling means is provided in the engine for cooling the internal combustion engine. In a vehicle equipped with a motor, and so on, such as a hybrid vehicle or an electric vehicle, a high-voltage battery and various power conversion devices are provided for driving a motor. As such high-voltage batteries and various power conversion devices, and so on, generate high temperature, cooling means is also provided in a vehicle equipped with a motor.
A water-cooled cooling system has been commonly used as a cooling means. This water-cooled cooling system circulates a coolant through a cooling passage and cools heated components. It is thus important to check whether the coolant is insufficient or not because the cooling system cannot operate properly if the coolant circulated in the cooling passage is insufficient.
However, the conventional method of checking coolant shortage is possible only when the vehicle speed is equal to or less than a specific vehicle speed, the voltage of the auxiliary battery is equal to or greater than a specific value, and the inclination of the road is equal to or less than a specific value. Therefore, when the above conditions are not satisfied, it is impossible to diagnose the shortage of the coolant, and accordingly, even if a fault occurred in which the coolant leaks during the running of the vehicle, the fault diagnosis is impossible. Since the coolant leakage described above can lead to a safety accident of the vehicle, it is necessary to develop a technique for diagnosing the state of the coolant even when the vehicle is running.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.